Ion channels dynamically regulate membrane permeability through their ability to open and close (gate) in response to various stimuli. Progress has been made in identifying and characterizing parts of channel proteins that are involved in this gating process including "sensors" that detect stimuli, and "gates" that regulate the flow of ions through the channel pore. However many questions remain concerning the conformational events and interactions that couple the action of sensors and gates. A comprehensive understanding of sensor/gate communication is likely to be of fundamental importance in understanding how channels normally work and how they are modulated by endogenous factors, drugs, or disease. To determine the nature of communication between sensors and gates we have studied the function of the BK-type Ca2+- activated K+ Channel (Slo1); a channel that senses both membrane voltage and intracellular Ca2+ as well as a variety of potential regulatory factors including intracellular Mg2+, Heme, and extracellular Cu2+. BK channels participate in physiologically important processes, and disruptions in their function or expression have been associated with diseases such as hypertension, epilepsy and cancer. Therefore an understanding of BK channel regulation may have direct implications for understanding disease mechanisms and developing more effective therapeutic options. Allosteric mechanisms exist by which the activation of sensors and the opening of the gate in BK channels appear to represent distinct events that strongly influence each other but can occur in isolation. Slo1 offers a unique opportunity to elucidate the functional properties and molecular mechanisms of sensor/gate communication. By studying the response of Slo1 to extreme stimuli and taking advantage of particular kinetic and steady-state properties of this channel we are able to study, in isolation, sensor activation, channel opening, and the coupling between sensor and gate. These methods and analytical tools will be applied to mutant Slo1 channels to identify residues and interactions that are involved in sensor/gate communication, and to understand how Mg2+, Heme and Cu2+ regulate BK channel activity. The results will be important, not only for understanding the gating and physiological regulation of BK channels, but also for elucidating how sensors and gates are coupled and gating is regulated in other ion channels. [unreadable] [unreadable]